The Organic Light Emitting Display (OLED) possesses many outstanding properties of self-illumination, low driving voltage, high luminescence efficiency, short response time, high clarity and contrast, near 180° view angle, wide range of working temperature, applicability of flexible display and large scale full color display. The OLED is considered as the most potential display device.
The OLED can be categorized into two major types according to the driving methods, which are the Passive Matrix OLED (PMOLED) and the Active Matrix OLED (AMOLED), i.e. two types of the direct addressing and the Thin Film Transistor (TFT) matrix addressing. The AMOLED comprises pixels arranged in array and belongs to active display type, which has high lighting efficiency and is generally utilized for the large scale display devices of high resolution.
The AMOLED is a current driving element. When the electrical current flows through the organic light emitting diode, the organic light emitting diode emits light, and the brightness is determined according to the current flowing through the organic light emitting diode itself.
As shown in FIG. 1, the driving circuits of the respective pixels in the present AMOLED pixel generally are a 2T1C structure, which is a structure comprising two thin film transistors and one capacitor. When such AMOLED pixel driving circuit works, the scan signal Scan controls the switch thin film transistor ST to be activated, and the data signal Data is transmitted to the gate of the drive thin film transistor T1 , and charges the capacitor C. The drive thin film transistor DT is activated, and the source of the drive thin film transistor DT is coupled to the anode of the organic light emitting diode OLED, and the current flows from the drive thin film transistor DT to the organic light emitting diode OLED to make the same emit light. Under the function of the capacitor C, the voltage level of the gate of the drive thin film transistor DT is not kept unit the image of the next frame is switched.
The AMOLED pixel driving property must be the same with one another in all positions of the display panel. However, in the practical situation, due to many reasons, such as the process difference, the usage environment change and aging, the respective MOLED pixel driving properties are not completely the same, which leads to the different brightnesses of the organic light emitting diode OLED as the same data signal is inputted to the AMOLED pixel and the influence to the display result. Therefore, it is required to sense the AMOLED pixel driving property and to compensate the data signal, correspondingly.
The external compensation technology of sensing the AMOLED pixel driving property and utilizing the external drive circuit of the display panel for compensation to promote the image quality and lifetime of the display panel has already appeared. The external compensation technology according to prior art utilizes the Analog to Digital Converter (ADC) to sense the AMOLED pixel driving property based on sensing the change of the anode voltage of the organic light emitting diode OLED and the change of the source voltage of the drive thin film transistor DT for compensating the inputted data signal. However, due to reasons of aging of the organic light emitting diode OLED or the drive environment change, the anode voltage of the organic light emitting diode OLED will be raised, and has possibility to exceed the input voltage range of the analog to digital converter. Accordingly, the anode voltage of the organic light emitting diode cannot be accurately sensed to influence the compensation result to the data signal.